Sorry for being so vague, it's exactly the opposite!

Within Zen Cart:

I need to run an iFrame with a payment module that uses it to connect to the processor. In this case I only need to pass checkout data, shopping cart contents as POST variables, only product info, description, price, quantities, plus a new field because I need to add shipping cost to their warehouse nothing else ...

That's why I was worried about compatibility issues, if a use a pure iFrame, as their system is designed to display my user page within this iFrame, there the customer will fulfill all his info, whatever payment and shipping method they choose, and personal data.
All within this iFrame.

So my question was, will it work or I better pass these parameters and vars using curl?